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Author Topic: Cutting compressed gas cylinders  (Read 6462 times)
Maets
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« on: October 14, 2012, 02:49:15 pm »

I have been asked to provide a little insight into cutting a compressed gas tank.  This is for information only and NOT a tutorial.  Do not attempt unless YOU know what YOU are doing!

Compressed gas tanks can be VERY dangerous.  Unless you know what was in the tank and know what you are doing, you should not go about cutting them.  I have had 7 close calls in 21 years.  Three of them because I didn't know what was in them or wasn't sure.  There are two types of gases to worry about, flammable and toxic.  Toxic gas must be disposed of properly.  Flammable gas must be completely removed before cutting.  Just opening the valve is not sufficient for either type of gas.  It is best to stick to tanks that contained non flammable and non toxic gases.   CO2, O2, N2, He, Argon and air are the most commonly available and safe to work with.

It is vital that you remove the valve from a tank before cutting to ensure the tank truly is depressurize. (just removing the valve on a flammable gas tank is not sufficient)  My other close calls generally relate to trying to cut a tank that still had the valve in it.

A band saw is probably the safest way to cut, but I use a plasma torch.
Any questions?
« Last Edit: October 14, 2012, 04:31:17 pm by Maets » Logged

Maets
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« Reply #1 on: October 14, 2012, 04:52:33 pm »

Should add that protect clothing and face shield are a must.  A full face shield has saved my beautiful looks on a number of occasions.  Goggles are nice, but a face shield is better.
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« Reply #2 on: October 14, 2012, 05:02:39 pm »

I used to vent the tank, remove the valve, fill with water, leave to stand for 24 hours, drain and leave to dry for another 24 hours before cutting.

I'd agree on the bandsaw to begin with, plasma cutters take a bit more skill.
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« Reply #3 on: October 14, 2012, 07:17:30 pm »


I would also add that tanks which have contained liquid fuels or acetylene should not be cut, welded or heated under any circumstances as they cannot be safely purged without specialist equipment.  Acetylene tanks in particular are very dangerous, even when 'empty'.



The reasons for this are thus :

-Acetylene gas is unstable when pressurised and to be stored safely must be dissolved in acetone in a porous medium within the tank. Therefore even an 'empty' acetylene tank still contains a substantial quantity of acetone and probably a certain amount of acetylene which cannot be easily removed.  Acetylene tanks should not be messed with in any way.

-Liquid fuels, particularly gasoline, can migrate into the pores of the cylinder itself. Washing with water is unlikely to remove all traces of the fuel and the heat from cutting can cause it to vaporise, filling the tank with a potentially explosive mixture.  Tanks suspected of containing liquid fuels should be steam cleaned and purged with inert gas during cutting or welding.

It is also easy to forget the potential dangers of oxygen. Elevated oxygen concentrations can cause otherwise safe materials to spontaneously combust and burn violently.

Any pressurised container should be considered a potential bomb. The energy stored in compressed gas is very large indeed. Cutting into a pressurised tank is likely to be a fatal mistake. The valve should be physically removed from the tank, not just opened, before even thinking about cutting it.

 
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« Reply #4 on: October 14, 2012, 08:47:26 pm »

Thanks for the information, very interesting.
As for me, I would find some cleaned empty tanks. (if I could find some)
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Wilhelm Smydle
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« Reply #5 on: October 14, 2012, 09:55:51 pm »

Another danger of the acetylene tanks is possible asbestos exposure.

Some old fire extinguishers also contain toxic gasses.

It's not something that can be rushed.
I start by opening the valve for several hours.
Then remove the valve and purge with water.
Then drain and let stand inverted.
A good jig saw can do the job at the hobby level by drilling a pilot hole.
A band saw works if you have one.
Plasma or an oxyfuel torch will also work.
Cut off wheels are a bad option it's to easy to snap the blades and send bits flying.

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Jedediah Solomon
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« Reply #6 on: October 16, 2012, 01:56:56 am »

Just to add a humorous anecdote {With a disclaimer; DON'T TRY THIS AT HOME!} many years ago, my dad's fuel tank on his Fargo {Later, a div. of Chrysler Corp} pickup truck High-centred on a very sharp rock, thus spilling the contents over a large area of other similar rocks, leaving him stranded with a trailer and box full of lumber. Embarrassed After disconnecting the trailer and hand stacking the rest of the lumber, we were able to get the truck away from the outcropping it was hung  up on leaving us with another problem... getting home! We called a friend who had a portable arc welder, and after dismounting the tank, we proceeded to his farm, After filling the tank,  {which was upside down, hole being at the bottom after all}  with water for a good hour or so, he drained it, took out the sending unit, inserted a flexible exhaust hose in it and attached the other end to his tailpipe, flooding the tank with inert gas. As he welded a strip of metal over the split, the tank was in no danger of explosion, and he told us that he used this method several times in the past, so we were confident in his abilities. What my father had failed to consider is that while he was unloading the lumber from the truck, he kept walking through the gasoline, a fact that totally slipped his mind until the heat from his burning leather boot caught his pant leg on fire.  Shocked I have never seen my dad remove anything as fast as he did that day. Moral of the story..... Keep your work area {And bystanders} devoid of any flammable materials when welding or using anything that produces heat! Wink
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« Last Edit: October 16, 2012, 02:02:44 am by Jedediah Solomon » Logged

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« Reply #7 on: October 18, 2012, 10:07:21 am »

The real question is, where do you get your tanks?
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Maets
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« Reply #8 on: October 18, 2012, 12:26:12 pm »

Tanks are hard to come by, especially in any kind of quantity.  I have offered before and will offer again free tanks that are 4" diameter by 20" long.  They CAN"T be used as tanks, but can be cut up and used for what ever you want.  I also can't go shipping them, but if you can make it to Maryland I'll gladly give you a trunk full.
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Angus A Fitziron
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« Reply #9 on: October 18, 2012, 12:28:21 pm »

Maets - I am currently interested in percussion after getting myself an African hand drum (djembe). Your bells strike me as a possible addition to a percussion kit. Whilst out walking one of the grandkids, I spotted an old fire extinguisher (a 9 litre water one) and rescued it from the ditch where it had been dumped. Balancing it on the push chair on the way home I tried to work out how to turn it into an awesome jet pack and decided it was probably too big and clumsy. 

However, it might be good as a bell! It had been discharged and I removed the valve, gauge and hose and cleaned it out. Do you think it will be thick enough metal to get a good chime (or does thickness not matter?) I will understand if you do not want to give out your hard earned knowledge - it is after all your livelihood, but a hint or two before I cut would be an encouragement!

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« Reply #10 on: October 19, 2012, 12:36:05 am »

Look for welding suppliers that hydro test their own tanks.
Some will sell bad tanks at scrap prices.
Talk with your local scrap yard about other tanks.
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Maets
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« Reply #11 on: October 19, 2012, 12:49:06 am »

Angus - the water fire extinguishers are very thin and probably not have much if any sound.  The high pressure tanks make the best bells.  It could be used as a rocket pack (I know someone who did) a little large, but not very heavy.

Whilhelm - some places will, but MANY will not.  Always worth a try.
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Shadow Of The Tower
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« Reply #12 on: December 11, 2012, 09:58:07 am »

So I finally have acquired some high pressure (2216 PSI) steel tanks and would like to make a bell out at least one of them.

What I have is a tank 6 3/4 diameter, about 3/8th thick and 17" tall. I already have the bottom cut off and the valve removed.

Any advice on the rest? How to get the best sound? stand recommendations?
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Maets
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« Reply #13 on: December 11, 2012, 02:37:36 pm »

Mostly there.  The edge should be smooth. The top should be a solid for hanging with  no vibration.  Stand options are limitless.
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